JPH01268352A - Color operating circuit for color printing - Google Patents

Abstract

PURPOSE:To quickly convert picture data expressed with R, G, and B to print picture data expressed with Y, M, and C by providing three accumulators where multiplication results successively outputted from three color conver sion coefficient multipliers are accumulated. CONSTITUTION:Multiplication between plural color variables R, G, B, R<2>, G<2>, B<2>, RG, GB, and BR generated from R, G, and B signals by a multiplexer 1 and a color variable multiplier 2 and respective corresponding color conversion coefficients aij and accumulation of multiplication results are simultaneously performed in parallel by color conversion coefficient multipliers 31-33 for respective colors Y, M, and C and accumulators 41-43. Thus, the processing time is shortened, and the color conversion processing is quickly executed though quadratic approximating expressions are used to perform color conversion, and common circuits can be used because color conversion coefficient multipliers 31-33 for respective color Y, M, and C and accumulators 41-43 have the same circuit constitution, and a color operating circuit for color printing is presented with a small size and a low cost.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a color calculation circuit for color printing that converts image data in RGB representation, which is the three primary colors of the additive color method, to image data for printing in MMC representation, which is the three primary colors of the subtractive color method. A multiplexer that sequentially selects image data of RGB expression from image data in a predetermined order, with the aim of converting image data of expression into image data of MMC expression for printing at high speed, and the selected image data. Based on 3 primary color variables R, G, B and 6 secondary color variables R2, G2
．． B2. RG, GB.

A color variable multiplier that sequentially creates and outputs BR, and a color variable multiplier provided for each YMC color that multiplies each sudden variable sequentially output from the color variable multiplier by a corresponding color conversion coefficient aiJ for each YMC color. 3 color conversion coefficient multipliers, and 3 accumulators that cumulatively add the multiplication results sequentially output from each color conversion coefficient multiplier and output the addition results as image data for each YMC color. Consists of.

[Industrial application field]

The present invention relates to a color calculation circuit for color printing that converts image data in RGB representation, which is the three primary colors of the additive color method, to image data for printing in MMC representation, which is the three primary colors of the subtractive color method.

[Conventional technology]

In recent years, computers have been widely used in the printing field to print color images. FIG. 2 shows the principle of this type of computer-based image processing system for color printing. A color original image to be printed is scanned into R (red), G (green), and B (blue) by a color scanner 51. It is separated into the three primary colors of the additive color method (light) and read into the processor 52, and this RGB display image data is used for printing in the three primary colors of the subtractive color method (paints): Y (yellow), 1M (magenta), and C (cyan). The image data is color-converted and stored in the magnetic disk 53, and image data for printing consisting of YMCK is obtained by adding K (black) data for image outline and brightness adjustment as necessary. There is.

The color image stored on the magnetic disk 52 is displayed on a CRT display 54 at any time, and the image is configured so that it can be freely modified on the CRT display. When printing a color image, the above magnetic disk 5
The plotter 55 uses the YMCK printing image data stored in the YMCK printing image data stored in the YMCK colors 56. , 56. , 56c, 56K are created,
Based on these four original films, printing original plates for each color of YMCK are made, and each printing original plate is used to overprint each color of MMCK on paper to print the desired color image. .

In the computer-based image processing system for color printing described above, image data in RGB representation consisting of the three additive primary colors optically read from the color scanner 51 is converted into printing image data in MMC expression consisting of the three subtractive primary colors. Conventionally, to perform this color conversion, the following linear approximation formula (1) or quadratic approximation formula (2) is used.
The processor 52 uses one of the calculation formulas
Generally, it was calculated sequentially using software.

[Problem to be solved by the invention]

However, when using the above-mentioned -order approximation, the amount of calculation is small, but the conversion order is insufficient to perform accurate color conversion, resulting in problems with color reproducibility.On the other hand, when using quadratic approximation, color reproduction Although this method has excellent performance, the problem is that the amount of calculation becomes enormous and the processing time becomes long.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a color calculation circuit for color printing that can rapidly convert RGB-expressed image data into MMC-expressed printing image data consisting of three subtractive primary colors. It is.

[Means to solve the problem]

The present invention, as shown in the principle embodiment in FIG. 1, realizes a color calculation circuit for color printing that can perform color conversion at high speed using the above-mentioned quadratic conversion formula (2). A multiplexer 1 that sequentially selects RGB-expressed image data from image data according to a predetermined order, and three primary color variables R, G, B, and 6 based on the selected image data.
secondary color variables R2°G2. B2. RG, GB,
A color variable multiplier 2 that sequentially creates and outputs SR, and a YM multiplier that multiplies each color variable sequentially output from the color variable multiplier by the corresponding color conversion coefficients a and J for each YMC color.
C Three color conversion coefficient multipliers 31 provided for each color
33, and cumulatively add the multiplication results sequentially output from each color conversion coefficient multiplier, and add the previous addition results to M
It is equipped with three accumulators 41 to 43 that output image data for each color of MC.

[For production]

In the color conversion coefficient multipliers 33 to 33, the nine color variables R1G, B, which are the second term on the right side of the quadratic approximation formula of equation (2), are stored.
R2, G2. B2. Color conversion coefficient a for each color of YMC in the first term on the right side corresponding to RG, GB, BR,
J is stored in advance as a coefficient table. That is, the color conversion coefficient multiplier 31 for Y color has nine color conversion coefficients for Y color ranging from 1st row and 1st column to 1st row and 9th column of the first term on the right side of equation (1). . . , a, 9 are color conversion coefficients for M color, and the color conversion coefficient multiplier 3□ for M color has nine color conversion coefficients a21 . . . . , al, and the color conversion coefficient multiplier 33 for color 0 has nine color conversion coefficients a33 .・・・
...,a,.

are stored respectively. These color conversion coefficients al are determined according to the characteristics of the printing ink of each Y, M, and C color used at that time, the type of printing paper, etc., and color conversion coefficients with different values are used for different printing targets. is common. Therefore, each color conversion coefficient a, J is RA
It is said that it can be stored and rewritten in a memory such as M.

Now, when RGB-expressed image data (hereinafter referred to as RGB signals) is input manually, the multiplexer 1 first selects the R signal and sends it to the color variable multiplier 2. The color variable multiplier 2 uses this R signal as a primary color variable R and uses it as a color conversion coefficient multiplier 33.
~ Send to 33.

Each of the color conversion coefficient multipliers 3I to 33 calculates color conversion coefficients a11-B2 for the color variable R with respect to the sent color variable R.
Multiply each by Is a3□. As a result, the multiplication value a+1R is output from the color conversion coefficient multiplier 33 for Y color.
The color conversion coefficient multiplier 32 for M color outputs multiplication values a, z+R.
However, from the color conversion coefficient multiplier 33 for color 0, the multiplication value a33
R is output and sent to accumulators 4-43, respectively.

The remaining primary color variables G and B are processed in the same way by the color variable multiplier 2.
are sent to each color conversion coefficient multiplier 33-33, each color variable G, B is incremented and multiplied by the corresponding color conversion coefficient aB, and each multiplied value is sent to each corresponding accumulator 4□-4.
3 and are cumulatively added to the previously added values stored in each accumulator 41 to 43.

After the color conversion processing of the three primary color variables R, G, B is completed, the six secondary color variables R2, G', B2. R
Execute color conversion processing for G, GB, and BR.

The color variable multiplier 2 squares the R signal from the RGB signal selected by the multiplexer 1 to create a secondary color variable R2, and sends this color variable R2 to each color conversion coefficient multiplier 31-33.

The color conversion multipliers 31 to 33 use this sent color variable R2.
, the color conversion coefficient a33 for the color variable R2.

B24v"34 respectively. As a result, the multiplication value azR2 from the color conversion coefficient multiplier 31 for Y color is
The output a24R2 from the color conversion coefficient multiplier 3□ is
Also, the output a34 from the color conversion coefficient multiplier 33 for color 0
R'' is output, and each multiplied value is sequentially sent to the corresponding accumulators 4□-43, and is cumulatively added immediately to the previous addition stored in each accumulator 41-43.

Similarly, the remaining secondary color variables G2. B2. R
G.

Similarly, GB and SR are sent from the color variable multiplier 2 to each color conversion coefficient multiplier 33 to 33, multiplied by the corresponding color conversion coefficient al, and sequentially sent to each corresponding accumulator 41 to 43. It is cumulatively added to the previously added values stored in each of the accumulators 4□ to 43.

As described above, three primary color variables R, G, B and six secondary color variables R', G'', B', RG, GB,
When the multiplication and integration of the color conversion coefficients a and J for BR are completed, the calculations for all elements on the right side of equation (2) are completed, and the registers 51 to 53 for each YMC color are filled with color conversion from RGB signals to MMC signals. Image data MMC for printing shown by equation 2) is obtained.

In addition, at the same time as the above 3 colors of MMC + K < black)
If it is desired to obtain the same by color conversion, the color conversion coefficient multiplier 31, accumulator 44, and register 54 may be connected in parallel as shown by the dotted line in FIG.

〔Effect of the invention〕

According to the present invention, RG B (a plurality of color variables R, G, B, R2, G2.82. RG, made from words)
Since the multiplication and cumulative addition of GB and BR with the corresponding color conversion coefficients a and j are simultaneously performed in parallel in the color conversion coefficient multiplier and accumulator for each color of YMC, processing time is shortened and the quadratic approximation formula Even though color conversion is performed using , color conversion processing can be executed at high speed.

In addition, since the color conversion coefficient multiplier and accumulator for each YMC color can have the same circuit configuration, the circuit can be shared, making this type of color calculation circuit for color printing compact and inexpensive. can be provided to

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a principle embodiment of the present invention, and FIG. 2 is a diagram showing an example of an image processing system for color printing using a computer. 1 is a multiplexer, 2 is a color conversion multiplier, 31 to 33 are color conversion coefficient multipliers for each YMC color, 41 to 43 are YMC
Accumulators for each color, R, G, 'B are image data consisting of red, green, and blue, which are the three primary colors in the additive color method, and Y, M, and C are image data, consisting of yellow, magenta, and cyan, which are the three primary colors in the subtractive color method. This is image data for printing.

Claims (1)

[Claims] A multiplexer (1) that sequentially selects RGB-expressed image data from image data according to a predetermined order; and three primary color variables R, G, and B based on the selected image data. 6 secondary color variables R^2, G^2, B^2
, RG, GB, and BR sequentially and output them; and a YMC multiplier that multiplies each color variable sequentially output from the color variable multiplier by a corresponding color conversion coefficient a_i_j for each YMC color. The three color conversion coefficient multipliers (3_1 to 3_3) provided for each color and the multiplication results sequentially output from each color conversion coefficient multiplier are cumulatively added, and the addition results are used as images for each YMC color. Three accumulators (4_1 to 4) that output as data
_3) A color calculation circuit for color printing, characterized by comprising: